Why? It would have been simplest for Ozai to kill her. But since he's not quite Azula, I would imagine she was exiled somewhere. Given how comfortable she was with the apparatus of imperial oppression, I would imagine that if she's still alive anywhere, she's probably a terrorist, arrested or killed for her efforts against the present Avatar.

Why? Because if so, there's no point in devoting a comic to it. There's no point in showing Zuko discovering it, or having the audience learned it. There's no resolution.

There would be plenty of resolution if she was imprisoned somewhere. And knowing she disapproved of what he'd done would be both crushing for the character and wonderful for the readers. It would be a real chance to appreciate how the insidious effects of privilege, and lets Zuko wrestle with the influence of family ties here that escapes the "honor" rubric that they treated more than thoroughly in the original series. If the first comic series looked at some of the complexity of post-imperial reconstruction, this would take it to the next level. It seems a sensible choice in many respects.

I'm sorry if this question has been answered already, but I'm assuming that there is no known release date for the next chapter, right? Wikipedia says 2013, but I saw that Cartoon Network released their press release and I noticed that Korra wasn't listed for the 2013 - 2014 season so I'm assuming the next chapter will be out for the 2014 - 2015 season?